The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Punch retainers can be used to retain a punch in a desired position. For example, punch retainers can be used in punch presses in the stamping industry to form and pierce various materials. Punch retainers enable the punches to be accurately positioned with respect to the complementary die and to be quickly and easily replaced without loss of the accurate punch position at set-up.
Punch retainers, in general, use socket-head cap screws and are a steel body that is bolted to die sets in which the punch is inserted into. The punch is retained by a spring-loaded ball that wedges into a detent in the punch and holds the punch during its utilization. The punches may use a backing plate across the entire bottom of the retainer or a plug behind the punch as its backing member. The use of either a backing plate across the entire bottom of the retainer or a plug behind the punch as its backing member results in a more complicated punch retainer and increases the number of parts. Moreover, the use of the extra parts can increase the cost of manufacturing and producing the punch retainer.
Typically, three or more dowels are used to position the retainer in a desired orientation so that the punch being held therein forms the aperture in a desired location. The preparation of three openings to receive the three dowels within the die retainer, however, is time consuming and increases the cost of producing the retainer. Typically, two or more fasteners are used to fasten the retainer to a press platen or die set. The preparation of two or more openings to receive the fasteners within the die retainer, however, is time consuming and increases the cost of producing the retainer. Additionally, the use of three or more dowels and two or more fasteners also increases the cost of preparing the press platen or die set in that these components also require complementary openings to receive the dowels and fasteners. Furthermore, the typical punch retainers have an exterior shape that is configured to align with other punch retainers. As such, these exterior shapes typically require machining of the exterior surface to form the punch retainers. This machining operation increases the cost of producing such retainers.
An improved punch retainer eliminating the need for the backing plate or plug behind the punch is disclosed in U.S. Pat. No. 5,357,835, assigned to the Assignee of the present invention and incorporated by reference herein. The improved retainer utilizes a blind flat bottom borehole for the punch receptacle. The bottom of the blind hole protects the press platen or die set from wear and impact damage. The punch hole is counterbored at the bottom to eliminate any fillet with the side wall and permit perfectly flat grinding to the periphery. The dowel pin hole centered on the centerline of the punch is formed directly in the retainer body, thus eliminating a source of inaccuracy arising from the separate backing plug and backing plate utilized in other punch retainers.
With a backing plate no longer being required, however, the oblique opening in the retainer within which the spring and ball lock are disposed is open to the exterior and exposed when the retainer is uninstalled. An undercut and a spring with an enlarged portion can be utilized to hold the spring in place when the retainer is uninstalled. The undercut and spring with an enlarged end is typically sufficient to hold the spring in. However, if forces are applied to the ball when the retainer is uninstalled, the spring can possibly release and may result in the spring and/or ball falling out of the retainer. A snap ring can be used to positively retain the spring within the aperture. The snap ring, however, is an additional expense and can be difficult to install and uninstall. Additionally, the forming of an undercut in the opening is another manufacturing expense. Moreover, the use of a spring with an enlarged end can cost more than a traditional spring having a uniform exterior dimension in similar-sized ends.
In accordance with the present teachings, a punch retainer can include a body with a punch-retaining passage and a spring passage. The spring passage can have an intersecting area with the punch-retaining passage and the spring passage can have a threaded section. A ball can be disposed in the spring passage. A spring can be disposed in the spring passage and can bias the ball toward the intersecting area. A threaded member can be disposed in the spring passage and can engage with the threaded section therein. The threaded member can compress the spring into the ball. The threaded member can retain the spring in the spring passage.
In another aspect of the present teachings, the punch retainer can include a body having a flat surface. A punch-retaining passage and a spring passage can be in the body and can have an intersecting area. A spring can be disposed in the spring passage and can bias a ball in the spring passage toward the intersecting area. There can be a single dowel passage for holding a locating dowel. The dowel passage can be coaxial to and of a smaller diameter than the punch-retaining passage. In yet another aspect, there can be a single fastener passage for receiving a fastener that attaches the retainer to a press platen or die set.
A retainer according to the present teachings is advantageous over traditional retainers in that a regular spring not requiring special features, such as an enlarged end, can be utilized to provide a ball lock for the punch. Avoiding a specialized spring can reduce the cost of the retainer. Moreover, the retainer can avoid the use of an undercut, thereby saving a manufacturing step. Furthermore, the retaining member for the spring can be adjusted to compensate for deterioration in the performance of the spring. The ability to compensate for deterioration in the performance of the spring can advantageously increase the useful life of the spring and result in a longer useful life of the retainer before the spring is replaced. Additionally, the axial alignment of the spring with the retaining member facilitates the manufacture of the oblique channel within which the spring, ball and retaining member are disposed. Moreover, the use of a single dowel and single hold-down fastener to position and hold the retainer in a desired orientation can advantageously simplify and reduce the manufacturing costs for the retainer. Moreover, the retainer according to the present teachings can be cylindrical in shape. The cylindrical shape advantageously facilitates the manufacture of the retainer from bar stock material as the bar stock material is already cylindrical in shape. Additional advantages and features of the present teachings will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings provided herein. It should be appreciated that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.